So, my dependencies are 
[root@proxy ~]# rpm -q --whatrequires 'perl(Compress::Zlib)'
perl-Filter-1.34-1.el4.rf
perl-Archive-Tar-1.56-1.el4.rf
spamassassin-3.3.1-52.el4
smeserver-spamassassin-2.0.0-3.el4.sme
(I tried the same with the other perl items but they seem not required by anything)
[root@proxy ~]# rpm -qi smeserver-spamassassin
Name        : smeserver-spamassassin       Relocations: (not relocatable)
Version     : 2.0.0                             Vendor: Contribs.org <http://contribs.org>
Release     : 3.el4.sme                     Build Date: lun 19 apr 2010 16:37:22 CEST
Install Date: gio 27 mag 2010 10:52:56 CEST      Build Host: build64-1
Group       : Networking/Daemons            Source RPM: smeserver-spamassassin-2.0.0-3.el4.sme.src.rpm
Size        : 6755                             License: GPL
Signature   : DSA/SHA1, lun 19 apr 2010 16:40:47 CEST, Key ID 3d7205081e9c9308
Packager    : Contribs.org <http://contribs.org>
Summary     : SME Server - spamassassin anti-spam module
Description :
SME Server - spamassassin anti-spam module
[root@proxy ~]# rpm -qi spamassassin
avvertimento: only V3 signatures can be verified, skipping V4 signature
Name        : spamassassin                 Relocations: (not relocatable)
Version     : 3.3.1                             Vendor: ATrpms.net
Release     : 52.el4                        Build Date: mer 31 mar 2010 22:27:53 CEST
Install Date: gio 27 mag 2010 10:52:24 CEST      Build Host: el4.atrpms.net
Group       : Applications/Internet         Source RPM: spamassassin-3.3.1-52.el4.src.rpm
Size        : 3367331                          License: Apache
Signature   : DSA/SHA1, gio 01 gen 1970 01:00:00 CET, Key ID 0000000000000000
Packager    : ATrpms <http://ATrpms.net/>
URL         : http://spamassassin.apache.org/
Summary     : Spam filter for email which can be invoked from mail delivery agents
not sure why I would have a perl-Filter-1.34-1.el4.rf or perl-Archive-Tar-1.56-1.el4.rf / it is possible they came with a wrongfully tried perl installation.. and:
Name        : perl-Filter                  Relocations: (not relocatable)
Version     : 1.34                              Vendor: Dag Apt Repository, http://dag.wieers.com/apt/
Release     : 1.el4.rf                      Build Date: Thu 11 Oct 2007 12:56:36 AM CEST
Install Date: Thu 27 May 2010 11:12:04 PM CEST      Build Host: lisse.leuven.wieers.com
Group       : Applications/CPAN             Source RPM: perl-Filter-1.34-1.el4.rf.src.rpm
Size        : 291881                           License: Artistic/GPL
Signature   : DSA/SHA1, Thu 11 Oct 2007 10:54:16 AM CEST, Key ID a20e52146b8d79e6
Packager    : Dag Wieers <dag@wieers.com>
URL         : http://search.cpan.org/dist/Filter/
Summary     : Perl module that implements Perl source filters
I find it strange though that there would be a spamassassin from atrpms.net.. or is that normal)
anyway I cant uninstall spamassassin.. obviously. 
sigh. 
so, if I eliminated perl-filter, found a newer version of spamassassin.. (which version is there in the contribs repos?) coult I stand any chance?
M